A multilayer ceramic capacitor has been widely utilized as an electric parts having small size and large capacitance with high reliability, and a plurality of such multilayer ceramic capacitors have been arranged in an electronic equipment
In recent years, there it has been required for the electronic equipment to provide a small-sized and a high reliability, and such requirement has also been desired for the multilayer ceramic capacitor so as to realize a down-sizing, a large capacitance, a low price and a high reliability.
The multilayer ceramic capacitor includes a layered dielectric body which is formed by alternately laminating dielectric layers and internal electrode layers external electrodes. Such layered dielectric body is formed by laminating two kinds of raw material layers i.e., one of the internal electrode layers and the other of the dielectric layers alternately, and simultaneously sintering the two kinds of the raw material layers together. Accordingly it is required for the raw material of the internal electrode layer to have a property not reactive to the raw material of the dielectric layer even if both raw material layers are sintered. For this reason, in a prior art, a noble metal such as platinum (Pt) or palladium (Pd) has been used for a material of the internal electrode layer. In recent years, in accordance with the increasing the need of large capacitance, it has been required for the multilayer ceramic capacitor to be incorporated with increasing number of the internal electrode layers. However, such noble metal is expensive and the use thereof is hence not reasonable in terms of cost.
In order to eliminate such a defective, it is realized that nickel (Ni), a cheep base metal material, is utilized as the material of the internal electrode layers, and there has been developed a dielectric material capable of being sintered in a reducing atmosphere in which the nickel is not oxidized and a sintering condition. As a result, remarkable cost-down in manufacturing such multilayer ceramic capacitor can be realized.
As mentioned above, according to the requirement for the electronic equipment to have a small-sized or miniaturized structure and the high reliability, it is also required for the multilayer ceramic capacitor as an electronic element to have a small-sized structure. However, the small-sized structure of the multilayer ceramic capacitor will result in a reduction of effective area.
The capacitance is generally expressed as this equation:C=∈o×∈s×n×S/d wherein C: capacitance (F); n: number of effective dielectric layers; ∈o: dielectric constant in vacuum condition; ∈s: relative dielectric constant; S: effective area (m2); d: thickness of dielectric layer(m).
In order to obtain substantially the same capacitance even if the multilayer ceramic capacitor is down sizing, it will be apparent from the above equation that it is essential to make thin dielectric layer and to increase the number of dielectric layers. However, a structural defect may easily occur by making thinning of the dielectric layer, and increasing the number of the laminated dielectric layers. This problem becomes prominent with increasing the number of the laminated dielectric layers, and much severe in recent technology in which the thickness of the dielectric layer becomes thinner and the number of the laminated dielectric layers becomes increased to satisfy the requirement of the small-sized structure and large capacitance thereof.
In order to solve such problems, various countermeasures have been considered and searched in various directions. For example, Japanese Unexamined Patent Publication (KOKAI) No. HEI 8-236386 shows a technology for improving mechanical strength by reducing compression residual stress to a value not more than 50 MPa. Another Japanese Unexamined Patent Publication No. WO 01-033588 discloses a technology of controlling expansion coefficients of the layered dielectric body in the laminating direction and the width direction thereof to be within predetermined ranges, respectively, by adjusting the amount of components in the internal electrodes to thereby prevent cracks and reduce defective fraction.